The invention relates to a method for supply of liquid for scale treatment and killing to a subsea well. More particularly it relates to a method for supply of liquids for scale treatment and killing to a subsea well, where the subsea well is provided with a tree which has a swab valve and a coupling for a tree cap. The invention also relates to a device for practicing the method.
During petroleum recovery it has proven necessary to supply liquid to wells in order to treat them, i.e. to prevent the formation of or remove scale. It has also proven necessary to be able to supply heavy liquid to the well for so-called killing.
According to prior art such work is carried out on subsea wells by removing a tree cap from a tree mounted on the subsea well by means of a suitable tool. Then a so-called “kill and scale” tool which has a hose connection to a vessel, is lowered and coupled to the tree, whereupon pumping of liquid into the subsea well may take place.
This prior art has several drawbacks. A considerable drawback is that the tree cap must be removed, which reduces the number of barriers between the well flow and the surroundings.
If a leakage in the valves of a subsea well such as a downhole safety valve is detected, it may be that the only barrier is the swab valve of the tree and the tree cap. Then, due to safety reasons, the tree cap cannot be removed.
The only possibility then is to supply heavy liquid via the production tubing, which implies that neighboring wells must also be shut down.
US-document 2003/0136927 describes a coupling for scale treatment and killing where the coupling is provided with a pressure balanced slide valve in order to avoid potentially large forces which may occur in such couplings.